Sheet conveying device and image forming apparatus

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 11/179,479, filed on Jul. 13, 2005, based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-209005 filed on Jul. 15, 2004, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a sheet-conveying device for conveying sheet such as paper and film and an image forming apparatus.

DESCRIPTION OF THE BACKGROUND

In an image forming apparatus such as an electrophotographic copier, a facsimile, and a printer, there is a sheet-conveying device, when supplying sheet such as sheet of paper and sheet-like films from a paper supply cassette device or a paper supply tray, for clamping the sheet by a separation sheet and a conveying roller or a separation roller and a conveying roller and supplying only the top of sheet. Further, there is a sheet-conveying device for clamping the sheet supplied and separated from the paper supply cassette device or paper supply tray by the conveying roller and a driven roller and conveying them in a predetermined direction. In such a sheet-conveying device, to stably convey sheet, in Japanese Patent Application 2002-356242, to pressurize a roller pair symmetrical left and right composed of a conveying roller and a driven roller, a constitution of pressuring the left and right shafts of the driven roller separately from each other using two springs is disclosed.

However, like the conventional device, when the driven roller is pressurized to the conveying roller using the left and right separate pressing means, the pressure of the driven roller to the conveying roller becomes imbalance due to variations in the left and right pressing means and the clamping and conveying force by the left and right conveying roller and driven roller pair becomes imbalance. Therefore, during conveyance, sheet is skewed, and conveying defects such as jamming and bending of front ends are caused, or the sheet must be greatly repositioned by an aligning roller. And when the repositioning by the aligning roller is not sufficient, a problem arises that the image quality is decreased due to image displacement. The same may be said with the conveying roller for separating and conveying only the top sheet.

Therefore, a sheet-conveying device and an image forming apparatus for causing no skewing when clamping and conveying sheet by the conveying roller and driven roller or the conveying roller and separating member, preventing conveying defects, repositioning surely the front ends of sheet at the position of the aligning roller, thereby obtaining good images are desired.

SUMMARY OF THE INVENTION

Accordingly, an advantage of the present invention is to provide a sheet-conveying device and an image forming apparatus for preventing skewing when clamping and conveying a sheet, repositioning surely the front ends of the sheet by the aligning means, and causing no jamming and image displacement.

To achieve the above advantage, one aspect of the present invention is to provide a sheet-conveying device comprising a fixing roller member having a fixed shaft, a load roller clamping sheet together with said fixing roller member, a pair of first and second pressure units to press between said fixing roller member and said load roller member, by applies load to said fixing roller member, and a elastic member bridged between said pair of pressure units to elastic uniformly said pair of pressure units.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic block diagram showing the copier of the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> is a schematic perspective view showing the conveying device of the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 3</figref> is a schematic arrangement diagram showing the conveying device of the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 4</figref> is a schematic block diagram showing to be supported condition of the driven roller shaft on the front side of the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 5</figref> is an illustration showing the principle of making the pressure of the driven roller to the conveying roller uniform on the front side and rear side of the first embodiment of the present invention,

<figref idref="DRAWINGS">FIG. 6-1</figref> is a schematic perspective view showing the separation and conveying device of the second embodiment of the present invention,

<figref idref="DRAWINGS">FIG. 6-2</figref> is a schematic arrangement diagram showing the separation and conveying device of the second embodiment of the present invention, and

<figref idref="DRAWINGS">FIG. 7</figref> is a schematic block diagram showing the support condition of the driven roller shaft on the front side of the second embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the first embodiment of the present invention will be explained in detail with reference to the accompanying drawings. <figref idref="DRAWINGS">FIG. 1</figref> is a schematic block diagram showing a copier <b>10</b>, which is an image forming apparatus using the sheet-conveying device, which is an embodiment of the present invention. The copier <b>10</b> has a cassette mechanism <b>3</b>, which is a paper supply unit having paper supply cassettes <b>3</b><i>a </i>and <b>3</b><i>b </i>for storing sheet of paper P, which are sheet supplied toward an image forming unit <b>2</b>, which is an image forming portion. Further, the copier <b>10</b> has a manual paper supply mechanism <b>4</b> having a manual separation and conveying device <b>4</b><i>c </i>for taking out sheet of paper P from a paper supply tray <b>4</b><i>a</i>, which is a paper supply unit by a manual pickup roller <b>4</b><i>b </i>and then separating and conveying the top of sheet of paper P. Further, the copier <b>10</b> has a reversing conveying path <b>5</b> for reversing sheet of paper P during double-side image forming. On the top of the copier <b>10</b>, a scanner <b>6</b> for reading a document image is mounted.

The scanner <b>6</b> has a platen glass <b>61</b>, a platen <b>62</b> for covering the platen glass <b>61</b>, an optical unit <b>63</b> for irradiating light onto a document and focusing reflected light from the document, and a CCD scanner unit <b>64</b> for reading light from the optical unit <b>63</b>.

The image forming unit <b>2</b>, around a photosensitive drum <b>11</b>, which is an image carrier, has a main charger <b>12</b> for uniformly charging the photosensitive drum <b>11</b>, an exposure position <b>13</b><i>a </i>of a laser exposure device <b>13</b> for forming a latent image on the charged photosensitive drum <b>11</b> on the basis of image data from the scanner <b>6</b>, a developing unit <b>14</b>, a transfer charger <b>16</b>, which is a transfer unit, a separation charger <b>17</b>, a cleaner unit <b>18</b>, and a discharging LED <b>19</b> according to the rotation of the photosensitive drum <b>11</b> in the direction of the arrow q.

On the downstream side of the image forming unit <b>2</b> in the direction of sheet of paper P, a fixing device <b>22</b>, which is a fixing unit for clamping and conveying the sheet of paper P by a heat roller <b>20</b> having a built-in heater lamp <b>20</b><i>a </i>and a press roller <b>21</b> and heating, pressurizing, and fixing a toner image is mounted. On the downstream side of the fixing device <b>22</b>, a paper ejection roller <b>24</b> for ejecting the sheet of paper P after fixing to a paper ejection tray <b>23</b> is mounted.

On supply conveying paths <b>7</b><i>a </i>and <b>7</b><i>b </i>from the paper supply cassettes <b>3</b><i>a </i>and <b>3</b><i>b </i>to the transfer charger <b>16</b>, pickup rollers <b>30</b><i>a </i>and <b>30</b><i>b </i>for taking out sheet of paper P, first and second separation-conveying devices <b>31</b><i>a </i>and <b>31</b><i>b</i>, which are sheet-conveying devices, first and second conveying devices <b>32</b><i>a </i>and <b>32</b><i>b</i>, which are sheet-conveying devices, and furthermore an aligning roller <b>33</b>, which is an aligning means are mounted. The supply conveying path <b>7</b><i>a </i>neighboring the image forming unit <b>2</b> has a first conveying path cover <b>8</b> indicated by hatching and the supply conveying path <b>7</b><i>b </i>neighboring the cassette mechanism <b>3</b> has a second conveying path cover <b>9</b> indicated by hatching. The first conveying path cover <b>8</b> rotates in the direction of the arrow m around a fulcrum <b>8</b><i>a</i>, thus the supply conveying path <b>7</b><i>a </i>can be opened. The second conveying path cover <b>9</b> rotates in the direction of the arrow n around a fulcrum <b>9</b><i>a</i>, thus the supply conveying path <b>7</b><i>b </i>can be opened.

Next, the first and second conveying devices <b>32</b><i>a </i>and <b>32</b><i>b </i>will be described in detail. Further, the first and second conveying devices <b>32</b><i>a </i>and <b>32</b><i>b </i>have the same structure, so that one of them will be explained. For example, the first conveying device <b>32</b><i>a</i>, as shown in <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, has a pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r</i>, which is a fixing roller member on the front side and rear side of a conveying roller shaft <b>40</b><i>c</i>, which is a fixed shaft linked with a drive motor (not drawn). At the opposite positions to the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r</i>, a pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r</i>, which is a load roller member is mounted on the front side and rear side. The pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r</i>, for example, is made of synthetic rubber and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r</i>, for example, is made of metal or resin. By the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r</i>, sheet of paper P are clamped and conveyed.

The pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>is attached free rotation at a driven roller shaft <b>41</b><i>c</i>, which is a load shaft. As shown in <figref idref="DRAWINGS">FIG. 4</figref>, for example, on the front side, the driven roller shaft <b>41</b><i>c </i>is supported by a slit <b>50</b><i>a </i>formed in a frame <b>8</b><i>b </i>in the first conveying path cover <b>8</b> and can slide in the slit <b>50</b><i>a</i>. At both ends of the driven roller shaft <b>41</b><i>c</i>, a guide <b>51</b><i>a </i>is formed. The guide <b>51</b><i>a </i>is inserted through the slit <b>50</b><i>a</i>, thus the rotation of the driven roller shaft <b>41</b><i>c </i>is fixed. By doing this, the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>can be driven to rotate stably by the pair of conveyer rollers <b>40</b><i>f </i>and <b>40</b><i>r. </i>

In the positions at the same distance from the centers of the driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>on the front side and rear side, a pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>in an L shape, which is a pair of first and second pressure units in the same shape on the front side and rear side, is arranged respectively. The pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>is arranged possible rotation respectively around fulcrums <b>43</b><i>f </i>and <b>43</b><i>r</i>. An L-shaped free end <b>44</b><i>f </i>of the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>on the front side makes contact and applies load with the driven roller shaft <b>41</b><i>c </i>at a pressure unit <b>45</b><i>f </i>on the front side, and a free end <b>44</b><i>r </i>on the rear side makes contact and applies load with the driven roller shaft <b>41</b><i>c </i>at a pressure unit <b>45</b><i>r </i>on the rear side, and the two free ends press the driven roller shaft <b>41</b><i>c </i>in the direction of the arrow x, which is the direction toward the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r. </i>

At hooks <b>46</b><i>f </i>and <b>46</b><i>r </i>formed on the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r</i>, one spring <b>47</b>, which is an elastic member is bridged. The spring <b>47</b> stretches the hook <b>46</b><i>f </i>on the front side in the direction of the arrow and the hook <b>46</b><i>r </i>on the rear side in the direction of the arrow t with the uniform force and gives the uniform press to the free ends <b>44</b><i>f </i>and <b>44</b><i>f </i>of the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>in the direction of the arrow x.

Here, to convey the sheet of paper P in the direction of in parallel with the arrow r, which is the conveying direction by the first conveying device <b>32</b><i>a</i>, the conveying force by the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>on the front side and rear side must be equal. To make the conveying force by the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>on the front side and rear side equal, pressure F on the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>by the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>on the front side and rear side must be equal.

Namely, for example, as shown in <figref idref="DRAWINGS">FIG. 5</figref>, on the basis of the center of the sheet of paper P in the conveying direction (hereinafter, abbreviated to PC), assumed the distance up to the center of a first fixing roller member A, which is the first position as L₁, the distance up to the center of a second fixing roller member B, which is the second position on the basis of the PC as L₂, the pressure applied between the first fixing roller member A and the load roller member C by the first pressure unit at center of the first fixing roller member A as F₁, and the pressure applied between the second fixing roller member B and the load roller member D by the second pressure unit at center of the second fixing roller member B as F₂, a formula of F=F₁L₁=F₂L₂must be held.

Therefore, in this embodiment as shown in <figref idref="DRAWINGS">FIG. 3</figref>, on the basis of the PC, the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>on the front side and rear side are laid out at the same distance toward the front and rear of the copier <b>10</b>. Further, the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>on the front side and rear side are laid out at the same distance toward the front and rear of the copier <b>10</b>.

Namely, assumed the distance up to the center of the conveying roller <b>40</b>f and the driven roller <b>41</b><i>f </i>from the PC on the front side as Lf, and the distance up to the center of the conveying roller <b>40</b><i>r </i>and the driven roller <b>41</b><i>r </i>from the PC on the rear side as Lr, a formula of Lf=Lr is held. Further, assumed the distance up to the free end <b>44</b><i>f </i>from the PC on the front side as lf, and the distance up to the free end <b>44</b><i>r </i>from the PC on the rear side as lr, a formula of lf=lr is held. Furthermore, the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>on the front side and rear side is attracted uniformly by one spring <b>47</b> and the force pressurizing the driven roller shaft <b>41</b><i>c </i>by the press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>is equal on the rear side and front side.

And, the distance from the center of the driven roller <b>41</b><i>f </i>on the front side to the press lever <b>42</b><i>f </i>on the front side and the distance from the center of the driven roller <b>41</b><i>r </i>on the rear side to the press lever <b>42</b><i>r </i>on the rear side are equal, so that the pressure on the front side and the rear side on the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>by the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>by the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>are equal. Namely, on the basis of the PC, the clamping and conveying force Pf of the sheet of paper P between the conveying roller <b>40</b><i>f </i>and the driven roller <b>41</b><i>f </i>on the front side and the clamping and conveying force Pr of the sheet of paper P between the conveying roller <b>40</b><i>r </i>and the driven roller <b>41</b><i>r </i>on the rear side are the same, that is, Pf=Pr.

Next, the operation of the present invention will be described. When the image forming process starts, the scanner <b>6</b> reads a document. In the image forming unit <b>2</b>, the photosensitive drum <b>11</b> rotates in the direction of the arrow q, thereby is uniformly charged by the main charger <b>12</b>, then is irradiated with a laser beam according to the document image by the laser exposure device <b>13</b>, and forms an electrostatic latent image. Next, the developing unit <b>14</b> develops the electrostatic latent image and a toner image is formed on the photosensitive drum <b>11</b>.

On the other hand, in the cassette mechanism <b>3</b> or the manual paper supply mechanism <b>4</b>, by the pickup rollers <b>30</b><i>a </i>and <b>30</b><i>d </i>or the manual pickup roller <b>4</b><i>b</i>, predetermined sheet of paper P are picked up. Then, while the picked-up sheet of paper P pass the separation-conveying devices <b>31</b><i>a </i>and <b>31</b><i>b </i>or the manual separation-conveying device <b>4</b><i>c</i>, only the top of sheet of paper is separated and is fed toward the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b. </i>

Then, the sheet of paper P separated by the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b </i>one by one reaches the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b </i>and is clamped and conveyed in the direction of the arrow r, which is the direction toward the aligning roller <b>33</b>. In the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b</i>, the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>are rotated in the direction of the arrow y, which is a conveying direction of the sheet of paper P by driving by the conveying roller shaft <b>40</b><i>c </i>by the drive motor and the pair of driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>making contact with the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>under pressure are driven to rotate and clamp and convey the sheet of paper P.

At this time, the pair of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and the driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>are arranged symmetrically on the basis of the PC and the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>are arranged symmetrically on the basis of the PC. So that, contact area of conveying rollers <b>40</b><i>f </i>and <b>40</b><i>r </i>and driven rollers <b>41</b><i>f </i>and <b>41</b><i>r </i>are arranged symmetrically on the basis of the PC. Furthermore, by the common spring <b>47</b>, the pair of press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>is given uniform tensile strength. Therefore, the clamping and conveying force Pf of the sheet of paper P by the conveying roller <b>40</b><i>f </i>and the driven roller <b>41</b><i>f </i>on the front side and the clamping and conveying force Pr of the sheet of paper P by the conveying roller <b>40</b><i>r </i>and the driven roller <b>41</b><i>r </i>on the rear side are the same, so that the sheet of paper P are not skewed, are kept straight, and reach the aligning roller <b>33</b>.

As mentioned above, during conveyance by the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b</i>, the sheet of paper P are not skewed, so that generally, the sheet of paper P are skewed little, and the dependence on repositioning of the sheet of paper P at the position of the aligning roller <b>33</b> is reduced, thus the aligning roller <b>33</b> can reposition the front ends of the sheet of paper P easily and surely.

After repositioning by the aligning roller <b>33</b>, the sheet of paper P is conveyed to the position of the transfer charger <b>16</b> in synchronization with a toner image on the photosensitive drum <b>11</b> and after transfer of the toner image, is separated from the photosensitive drum <b>11</b> by the separation charger <b>17</b>. After separation of the sheet of paper P, the photosensitive drum <b>11</b> is cleaned residual toner by the cleaner unit <b>18</b>, is removed the residual charge by the discharging LED <b>19</b>, and waits for the next image forming process. The sheet of paper P separated from the photosensitive drum <b>11</b> and having an unfixed toner image is inserted through the heat roller <b>20</b> and the press roller <b>21</b> of the fixing device <b>22</b> and after the toner image is heated, pressurized, and fixed, is ejected to the paper ejection tray <b>23</b>.

In this embodiment structured like this, in the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b</i>, on the basis of the PC, Lf=Lr and If =Ir and the tensile strength of the spring <b>47</b> bridged between the press levers <b>42</b><i>f </i>and <b>42</b><i>r </i>is the same. From this, the clamping and conveying force Pf of sheet of paper P by the conveying roller <b>40</b><i>f </i>and the driven roller <b>41</b><i>f </i>on the front side and the clamping and conveying force Pr of sheet of paper P by the conveying roller <b>40</b><i>r </i>and the driven roller <b>41</b><i>r </i>on the rear side are the same, that is, Pf=Pr.

Therefore, the sheet of paper P clamped and conveyed by the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b </i>is not skewed by the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b </i>and the good conveying can be improved. Further, the dependence on repositioning skewing of the sheet of paper P by the aligning roller <b>33</b> can be reduced, and the sheet of paper P can be repositioned surely before image forming, thus an image forming apparatus free of image displacement and of high image quality is obtained.

Next, the second embodiment of the present invention will be explained. The second embodiment is different in the constitution of the separation-conveying device from the first embodiment. Therefore, in the second embodiment, the same numerals are assigned to the same parts as those of the constitution explained in the first embodiment and the detailed explanation will be omitted. The first and second separation-conveying devices <b>31</b><i>a </i>and <b>31</b><i>b </i>of this embodiment have the same structure, so that one of them will be explained. As shown in <figref idref="DRAWINGS">FIG. 6-1</figref> and <figref idref="DRAWINGS">FIG. 6-2</figref>, the separation device has a separation roller <b>60</b>, which is a load roller member on a separation roller shaft <b>60</b><i>c</i>, which is a load shaft. The separation roller <b>60</b> is rotated in the direction of the arrow f, which is a separating direction of the sheet of paper P by prescribed driving force when the sheets of paper P are separated, to return the sheets of paper P picked up from the paper supply cassettes <b>3</b><i>a </i>or <b>3</b><i>b </i>by the pickup rollers <b>30</b><i>a </i>or <b>30</b><i>b </i>toward the paper supply cassettes <b>3</b><i>a </i>or <b>3</b><i>b. </i>

At the opposite positions to the separation roller <b>60</b>, a paper supply roller <b>61</b>, which is a fixing roller member is mounted. The paper supply roller <b>61</b> is rotated by a paper supply motor (not drawn) in the direction of the arrow g, which is a conveying direction of the sheet of paper P and supplies the top of the sheet of paper P picked up from the paper supply cassette <b>3</b><i>a </i>or <b>3</b><i>b </i>toward the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b</i>. The paper supply roller <b>61</b> is carried out to the paper supply roller shaft <b>61</b><i>c</i>, which is a fixed shaft driven in the direction of arrow g. As shown in <figref idref="DRAWINGS">FIG. 7</figref>, the separation roller shaft <b>60</b><i>c </i>is supported by a slit <b>103</b><i>a </i>formed in a frame <b>103</b> in the cassette mechanism <b>3</b> and can slide in the slit <b>103</b><i>a</i>. Therefore, the separation roller shaft <b>60</b><i>c</i>, although it slides in the slit <b>103</b><i>a</i>, is connected to the driving force via a link mechanism.

As shown in <figref idref="DRAWINGS">FIG. 6-2</figref>, a center of contact area of the separation roller <b>60</b> and the paper supply roller <b>61</b> will be defined if it is on the PC. In the positions at the same distance (If=Ir) from the centers of the separation roller <b>60</b>, a pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>in an L shape, which is a pair of first and second pressure units in the same shape on the front side and rear side, is arranged respectively. The pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>is arranged possible rotation respectively around fulcrums <b>63</b><i>f </i>and <b>63</b><i>r</i>. An L-shaped free end <b>64</b><i>f </i>of the press lever <b>62</b><i>f </i>on the front side makes contact and applies load with the separation roller shaft <b>60</b><i>c </i>at a pressure unit <b>65</b><i>f </i>on the front side, and a free end <b>64</b><i>r </i>of the press lever <b>62</b><i>r </i>on the rear side makes contact and applies load with the separation roller shaft <b>60</b><i>c </i>at a pressure unit <b>65</b><i>r </i>on the rear side. And the two free ends of the press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>press the separation roller shaft <b>60</b><i>c </i>in the direction of the arrow i, which is the direction toward the paper supply roller <b>61</b>.

At hooks <b>66</b><i>f </i>and <b>66</b><i>r </i>formed on the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r</i>, one spring <b>67</b>, which is an elastic member is bridged. The spring <b>67</b> stretches the hook <b>66</b><i>f </i>on the front side in the direction of the arrow j and the hook <b>66</b><i>r </i>on the rear side in the direction of the arrow k with the uniform force and gives the uniform press to the free ends <b>64</b><i>f </i>and <b>64</b><i>f </i>of the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>in the direction of the arrow i.

To supply the sheet of paper P separated one by one in parallel toward the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b</i>, the separation roller <b>60</b> and the paper supply roller <b>61</b> are arranged symmetrically on the basis of the PC. Further, the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>on the front side and rear side is also arranged symmetrically on the basis of the PC. Furthermore, the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>is attracted uniformly by one spring <b>67</b>, so that the force pressurizing the separation roller shaft <b>60</b><i>c </i>by the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>is equal on the rear side and front side. Therefore, the pressure of the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>on the front side and rear side on the paper supply roller <b>61</b> of the separation roller becomes equal.

In the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b</i>, when separating the sheet of paper P picked up by the pickup rollers <b>30</b><i>a </i>or <b>30</b><i>b</i>, the separation rollers <b>60</b> is rotated in the direction of the arrow f so as to return the lower sheet of paper P toward the paper supply cassettes <b>3</b><i>a </i>or <b>3</b><i>b</i>. The separation roller <b>60</b> makes contact with the paper supply roller <b>61</b> by the pressure of the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r</i>. On the other hand paper supply roller <b>61</b> is rotated in the direction of the arrow g by driving by the paper supply roller shaft <b>61</b><i>c </i>by the paper supply motor, and supply only the top of the sheet of paper P toward the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b. </i>

At this time, the paper supply roller <b>61</b>, the separation roller <b>60</b>, and the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>are arranged symmetrically on the basis of the PC. Furthermore, by one spring <b>67</b>, uniform tensile strength is given to the pair of press levers <b>62</b><i>f </i>and <b>62</b><i>r</i>. Therefore, the separation-conveying force of the sheet of paper P by the supply roller <b>61</b> and the separation roller <b>60</b> on the front side and the rear side become equal, and the sheet of paper P are not skewed, are kept straight, and reach the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b. </i>

As mentioned above, during conveyance by the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b</i>, the sheet of paper P are not skewed, so that the dependence on repositioning of the sheet of paper P at the position of the aligning roller <b>33</b> is reduced, thus the aligning roller <b>33</b> can reposition the front ends of the sheet of paper P easily and surely. Hereafter, the sheet of paper P, in the same way as with the first embodiment aforementioned, are clamped and conveyed toward the aligning roller <b>33</b> by the first or second conveying device <b>32</b><i>a </i>or <b>32</b><i>b. </i>

In this embodiment structured like this, in the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b</i>, the paper supply roller <b>61</b>, the separation roller <b>60</b>, and the press roller pair <b>62</b><i>f </i>and <b>62</b><i>r </i>are arranged symmetrically on the basis of the PC and the tensile strength of the spring <b>67</b> applied between the press levers <b>62</b><i>f </i>and <b>62</b><i>r </i>is the same. From this, the separation-conveying force of the sheet of paper P by the paper supply roller <b>61</b> and the separation roller <b>60</b> on the front side and the rear side become equal.

Therefore, the sheet of paper P separated and conveyed by the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b </i>are not skewed by the first or second separation-conveying device <b>31</b><i>a </i>or <b>31</b><i>b </i>and the good conveying can be improved. Further, the dependence on repositioning skewing of the sheet of paper P by the aligning roller <b>33</b> can be reduced, and the sheet of paper P can be repositioned surely before image forming, thus an image forming apparatus free of image displacement and of high image quality is obtained.

Further, the present invention is not limited to the aforementioned embodiments and can be changed within a range, which is not deviated from the object of the present invention. For example, if the pressure unit can give uniformly the pressure between the fixing roller member and the load roller member, the shape and structure thereof are not restricted. Further, the number of the fixing roller member or the load roller member is not limited. Further, the elastic member is not limited to the spring and it may be rubber or a steel wire bridged between the pair of pressure units. Furthermore, the sheet-conveying device is not limited to the use location if it is a place requiring conveyance of sheet, that is, it may be used in the reversing path or for conveying sheet by the scanner, and is not limited to the copier.

As described above in detail, according to the present invention, the fixing roller member and the load roller member stably can clamp and convey sheet or can separate and convey sheet without skewing them. Therefore, conveying defects such as jamming and bending in the conveying path of sheet are prevented, and a sheet-conveying device of good conveying is obtained, and the dependence on repositioning skewing of the sheet by the aligning means can be reduced, and the sheet can be repositioned surely by the aligning roller, thus an image forming apparatus free of image displacement and of high image quality is obtained.